Adhesive compositions are very well known. Generally, these compositions comprise of a thermoplastic elastomer, such as a styrenic block copolymer, a tackifying resin and a processing oil. Adhesives are generally produced either by dissolving all the ingredients in a common solvent capable of dissolving all the ingredients or by a hot melt process where the ingredients are melt processed at an elevated temperature.
During the production of adhesives, the polymer, tackifying resin and oil can be added as separate ingredients or the polymer and oil can be premixed then added together with the resin. When separate addition is utilized, the polymer is referred to as a neat or unoiled polymer. A common problem is that the neat polymer is difficult to mix, resulting in longer mixing times. Long mixing times is a disadvantage in the production of adhesives whether from solvent or hot melt process. In hot melt mixes in particular, if the mixing time is long the copolymer degrades during melt processing to generate lower molecular weight species. This degradation occurs due to the presence of oxygen, and due to shear degradation of the high viscosity copolymers. If the resulting degradation is severe, the resulting adhesive is no longer useful for the intended application.
Presoaking the polymer in oil or premixing the oil and polymer prior to their use in producing adhesives are alternative methods which are known in the art. However, these methods have not been utilized in the production of adhesives based on styrene-isoprene-styrene (SIS) block copolymer. One reason for this is that SIS block copolymers are too soft for handling. Thus, addition of oil prior to processing makes these block copolymer excessively tacky. Another reason is that with presoaking, an extra step is involved or required.
Thus, there continues to exist a need for improved methods of processing oiled SIS polymers in order to facilitate the production of good quality SIS polymer based adhesive compositions.